OK, found my instructions on using the Kensington Track Ball Pro with Keyboard Maestro. Just had to search on the name of the track ball to find it. Original for this particular document was dated 2012. It won't work with Catalina of course but it does for Mojave. Enjoy.
The Kensington Expert Mouse PRO and the Mac do work together. Including all 6 DIRECT LAUNCH buttons, and the 4 mouse buttons around the track ball. I haven't figured out how to get the scroll wheel to work, but that can most likely work as well. You do NOT need the Kensington software in order to make it work either. My solution was to use Keyboard Maestro purchased from their web site. I have used all the MAC OS up to the current Mojave and it works great. Those 6 program buttons are awesome!
First a note about Keyboard Maestro. To run correctly, it can't be sandboxes. You need to purchase it directly from the developer. They are www.stairways.com.
Second, the Kensington does fully work, all buttons, so you will get the Expert Mouse pro working just fine.
Load and launch Keyboard Maestro. (KBM). Launch the editor. The bug with Keyboard Maestro is you need to put a pause in between each command. I use a .5 second command. IN ADDITION, when you want to type text of some kind, do not tell Keyboard Maestro to paste in the text, have it TYPE it in. You get that option. If you follow both my rules above, your expert mouse pro will work. Keyboard Maestro also replaces my Quickeys 4.0, but that is another story.
I will offer an example to make the button at the top right of the track ball a double click. I am not a TEC writer, so I will do my best. Launch KBM. First click on the bottom left plus sign to add a Group. Rename it to MACROS FOR ALL PROGRAMS. Create a shortcut with KBM by clicking the center plus sign for ADD MACRO. Give it a name. I called mine DOUBLE CLICK. If you look closely you will see a green plus sign with the command NEW TRIGGER. Click it to open a pull down menu. The second from the bottom option is DEVICE TRIGGER. You will be using this option for all the track ball functions to work. Notice the blue box that shows up and says NONE. While it is blue, press the button that is the top right button of the track ball, or any button you want to become a double click on the Kensington Expert Mouse, (KEM). The word NONE is replaced with USB/PS2 WHEEL MOUSE BUTTON 5. Now, YOU ARE NOT DONE! Just to the right, is a double arrow and next to it are the words that say IS PRESSED. Click on the words and change them to IS RELEASED. OK, you now have a button on the Expert Mouse programed, but it is doing nothing. Now you need to do your first action. The first action must be a PAUSE. If you don't put one, KBM sometimes does not work. To put a pause in, click on the DISPLAY HIDE ACTION LIST plus sign at the bottom right plus sign. On the left, click on the folder called CONTROL FLOW. The list of actions the first item is PAUSE. double click it. Change the time from 1.5 seconds to .5 seconds. In the Categories section click on INTERFACE CONTROL. In the center, double click on MOVE OR CLICK MOUSE. This action will show up in the right window. You need to make 4 changes here. Where it says CLICK, click on it and change it to DOUBLE CLICK. Where it says FRONT WINDOW'S TOP LEFT CENTER click on it and change it to CURRENT MOUSE LOCATION. And as a CyA, click on bot box that says RESTORE MOUSE LOCATION.
Your KEM now does a double click when you press the top right mouse button.
To type text, or what ever, using the direct launch buttons, at the step for new trigger, push the direct launch button of your choice. Instead of a mouse click, insert an INSERT TEXT command and type your text. Remember, KBM has some trouble to PASTE correctly, so change the command to TYPE IT IN, as instructed above. If you have any questions, or have any cool macros that can do really great things with you KEM, please email me back at firstname.lastname@example.org. Put EXPERT MOUSE in the subject and it will get read.